[2.1 Docs] Identity, access and permissions #718

Parent for all 2.1 documentation work on Identity, access and permissions. Each sub-issue is one pull request; close the parent when all sub-issues are closed.

Sub-issues

• [2.1 Docs] Auth & Deployment: Email-first identity (breaking) + FIPS mode #528 [2.1 Docs] Auth & Deployment: Email-first identity (breaking) + FIPS mode
• [2.1 Docs] Identity, access, deployment and search configuration #633 [2.1 Docs] Identity, access, deployment and search configuration
• [2.1 Docs] Identity, access, deployment and search configuration #674 [2.1 Docs] Identity, access, deployment and search configuration
• [2.1 Docs] Platform: Domain assignment rules #688 [2.1 Docs] Platform: Domain assignment rules
• [2.1 Docs] Platform: Permission enforcement changes #689 [2.1 Docs] Platform: Permission enforcement changes
• [2.1 Docs] Platform: SSO and user management #690 [2.1 Docs] Platform: SSO and user management

Part of the 2.1 documentation tracker: #587